Direct current electromagnetic pump



Nov. 5, 1957 A. H. BARNES 2,311,923

DIRECT CURRENT ELECTROMAGNETIC PUMP Filed June 25, 1953 v 3 Sheets-Sheet 1 4 F/G. 2 M

F/Gl "K 96 F/G. 8

INVENTOR.

BY ARTHUR H. BARNES A TTORNE Y Nov. 5, 1957 A. H. BARNES v DIRECT CURRENT ELECTROMAGNETIC PUMP 3 Sheets-Sheet 2 Filed June 25, 1953 I NVENIOR. ARTHUR H. BARNES V ATTORNE'Y Nov. 5, 1957 A. H. BARNES DIRECT CURRENT ELECTROMAGNETIC PUMP 5 Sheets-Sheet 3 Filed June 25, 1953 INVENTOR. ARTHUR H. BARNES ATTORNEY United States Patent DIRECT CURRENT ELECTROMAGNETIC PUMP Arthur H. Barnes, Downers Grove. Ill., assignor to the United States of America as represented by the United States Atomic Energy Commission Application June 25, 1953, Serial No. 364,114

Claims. (Cl. 103-1) This invention relates to electromagnetic pumps that use direct current.

Liquid metals are singularly adapted to serve as heattransfer agents at elevated temperatures. Though water is a satisfactory medium of heat exchange for operations at normal temperatures, it is not satisfactory above 500 F., because of a high vapor pressure and a tendency to disintegrate into hydrogen and oxygen. Metals have higher boiling points and consequently negligible vapor pressures. In addition, the higher temperature conductivity of metal yields higher heat-transfer coefficients. In view of these properties, liquid metals are particularly suitable as coolants for high temperature operations.

The interest in liquid metals as coolants has served to spur the development of pumping equipment capable of handling such metals. Conventional positive displacement pumps have proven unsatisfactory due to the problems of designing bearings and seals to operate in liquid metals. The lack of bearings and seals in an electromagnetic pump makes it particularly desirable for pumping liquid metals in a closed heat exchange system.

The basis for the use of electromagnetic pumps with liquid metal is the fact that metals are electrical conductors. This fact makes possible the use of the motor lefthand rule upon which operation of the pump is based. A conduit for liquid metal is inserted into the gap between the poles of a magnet on two opposite sides, and between two electrical conductors on the other opposite sides. The crossing of the magnetic flux and the electric current at substantially right angles creates a longitudinal thrust in the liquid metal causing it to move through the conduit.

It is the object of this invention to improve the efficiency of electromagnetic pumps by adjusting the intensity of the magnetic field and the current flowing across the conduit.

Other objects will become apparent from the following description and the drawings in which:

Fig. 1 is a vertical sectional view, partly in elevation, of the electromagnetic pump of the present invention;

Fig. 2 is a horizontal sectional view taken on the line 2-2 of Fig. 1;

Fig. 3 is a vertical sectional view taken on the line 33 of Fig. 1;

Fig. 4 is an elevational end view;

Fig. 5 is an elevational view of one of two coils used in the pump;

Fig. 6 is an end view of the coil shown in Fig. 5;

Fig. 7 is an enlarged fragmentary sectional view showing a fluid-tight joint between certain parts of the pump; and

Fig. 8 is an enlarged fragmentary sectional view of one end of the pump conduit showing the manner in which the downstream end is disposed within a pipe with which it is connected.

As shown in Fig. 1, the electromagnetic pump constituting one embodiment of the present invention is generally indicated at 10. The pump is supported by a base plate 2,811,923 Patented Nov. 5, 1957 ice 12 which in turn is upheld by legs 14. Referring to Fig. 3, the pump is spaced from the plate 12 by means of three parallel ribs 16 and a pump frame 18 which rests on the ribs and by which the several parts of the pump are held together. The frame 18 consists of a pair of outer plates 20 and 22 which extend vertically from the two outer ribs 16, and of a pair of plates 24 and 26 which are horizontally disposed between the plates 20 and 22. As shown in Fig. 3 the plates 24 and 26 are attached to the upper and lower extremities of the plates 20 and 22 by means of bolts 28 to form the rectangular frame 18.

Central of the pump 10 and along the longitudinal axis thereof is disposed a conduit 30 through which the liquid being pumped (not shown in the drawings) is conducted and which is shown in Figs. 1, 2, and 3. The conduit 30 is composed of a material such as stainless steel, which is corrosion-resistant at high temperatures and has the property of high electrical resistivity. Throughout most of its length the conduit 30 is rectangular in cross-section and may be fashioned from an originally round tube. The precise details of the configuration of the conduit will be set forth in greater detail hereinbelow.

As shown in Figs. 2 and 3, the conduit 30 is disposed between two magnet cores 32 and 34 which lie to the left and right, respectively, of the conduit as shown in Fig. 3. The cores may be of soft iron. The core 32 is secured to the plate 20, and the core 34 to the plate 22 by means of bolts 36. Field windings for the cores 32 and 34 consist of coils 42 and 44, respectively, each of which makes one complete turn around its corresponding core. The coil 42 is provided with a connector 46 extending from its lower surface, and the coil 44 is provided with a connector 48 extending from its upper surface. Each connector is integral with its corresponding coil. Both coils are identical in configuration, and the coil 44 is separately shown in Figs. 5 and 6 with its connector 48 extending upright therefrom. It is to be noted that the coil makes one complete turn to form a central aperture 49, the dimensions of which are slightly greater than the dimensions of the core 34. The coil 42 has a similar aperture (undesignated) which is slightly greater in dimensions than the core 32. It is preferred that the cross-sectional dimensions of the coil be about 6 inches by 6 inches and that the coil consist of copper bar material. However, the cross section may be 4 inches by 4 inches in which event the coil makes two complete turns. The coil 44 has opposed end portions 50 and 51 separated by a narrow space 52. The end portion 51 merges directly with the connector 48. The end portion 50 is remote from the connector 48 and is provided with openings 53 for attaching bolts. As was stated above, the coil 42 is identical with the coil 44 in the pump in the position that would result if the coil 44 shown in Fig. 5 were revolved about a horizontal axis in or parallel to the plane of the paper. Referring to Figs. 1 and 3, the manner in which the coils 42 and 44 are disposed about the cores 32 and 34 and within the frame 18 is shown. Between the coils 42 and 44 is disposed a pair of conductors 54 and 56 which are oppositely disposed above and below the conduit 30. The conductor 54 is adjacent the spacer plate 24 and is provided with apertures aligned with the apertures 57 for the purpose of attaching the conductor to the coil 44 by means of bolts 53, which may be formed of stainless steel and are threaded into stainless steel nuts 58 set in the conductor 54. The contacting surfaces of the conductor 54 and the end portion 50 of the coil 44 are joined in a good current-conducting bond formed, for example, by silver soldering or silver brazing. The conductor 54 extends along the end portion 51 of the coil 44 and adjacent portions but is insulated therefrom as indicated at 59 in Fig. 3. The conductor 56 is associated with the coil 42 in the way in which the conductor 54 has just been described as being associated with the coil 44. The conductor 56 is bonded as by silver soldering or silver brazing to the end portion of the coil 42 remote from the connector 46 and is joined to said end portion by bolts 53 and nuts 58, which may be formed of stainless steel. The conductor 56 is insulated from the end portion of the coil 42 adjacent the connector 46 and adjacent portions as indicated at 60 in Fig. 3. Conductor 54 is insulated from coil 42 as indicated at 61 in Fig. 3. Conductor 56 is insulated from coil 44 as indicated at 62 in Fig. 3.

As shown in Fig. 1, conductors 54 and 56 extend along the conduit 30 and are secured to a portion 63 of the conduit in current-conducting bonds formed, for example, by silver soldering or silver brazing. The conduit portion 63 is longitudinally displaced from the end portions of the coils 42 and 44 to which the conductors 56 and 54 are bonded. The conductors 54 and 56 are elsewhere insulated from the conduit 30 as indicated at 64 and 65 in Fig. 1.

The conduit 30 is seen in Figs. 1 and 2 to vary in dimensions along its length, but the significant variation in dimension comes at the region 63. Referring to Fig. 2, it is assumed that the direction in which fluid is moved by the pump is from left to right as viewed in Fig. 2. Accordingly, the cores 32 and 34 are so shaped that the spacing between them decreases in the direction of flow (from left to right in Fig. 2). The width of the conduit portion 63, which is closely spaced from the cores 32 and 34, being insulated therefrom as indicated at 66 and 67, correspondingly decreases. Beyond the ends of the conduit region 63 the cores 32 and 34 have surfaces 68 and 69 which angle away from the conduit 30 and surfaces 70 and 71 which generally parallel the conduit 30, so that the spaces between the cores and the conduit beyond the region 63 increase in amount and then remain generally constant. The reasons for this shaping of the cores 32 and 34 and the conduit region 63 will be stated presently.

The core 32 is insulated top and bottom from the coil 42 as indicated at 72 in Fig. 3 and at its ends from the coil 42 as indicated at 73 in Fig. 2. The coil 34 is in sulated top and bottom from the coil 44 as indicated at 74 in Fig. 3 and at its ends from the coil 44 as indicated at 75 in Fig. 2. As shown in Fig. 2, the coil 42 has insulation 76 and 77 on the side toward the conduit 30 and the coil 44 has insulation 78 and 79 on the side toward the conduit 30. The coil 42 is insulated from the plate 20 as indicated at 80 in Fig. 3, and the coil 44 from the plate 22 at 81. The plate 24 is insulated from the coils 42 and 44 and the conductor 54 as indicated at 82 in Fig. 3. The plate 26 is insulated from the coils 42 and 44 and the conductor 56 as indicated at 83 in Fig. 3.

The metal to be pumped through the conduit 30 may be liquid sodium or a sodium-potassium alloy in liquid condition. Inasmuch as a large direct current is required for the operation of the pump, the terminals 46 and 48 are separately attached to bus bars (not shown) of sufficient size for the current supplied. Since the efficiency of the pump depends to a considerable extent upon the magnitude of the power required to maintain the magnetic field, considerable effort has been expended in constructing magnets with low power dissipation. The field windings or coils 42 and 44 are connected in series with the conductors 54 and 56 and close clearances are maintained between the coils and the corresponding cores. Although the pump is operated at relatively high currents, the voltage is low. The various insulators previously described may be formed of mica sheets.

At a given value of current and pressure there is an optimum value of magnetic field intensity for which the flow will be a maximum. This is due to the bypassing of current that becomes more pronounced in the conduit 30 as the counter electromagnetic force increases with increasing field. Increasing the length of the magnet poles 32 and 34 extends the path which the current must follow in the liquid to cross the conduit beyond the field region. By experiment it was found that when the pole length is increased beyond a certain dimension the efliciency of the pump is not increased proportionally. This is due to the retarding effect of the induced current developed in the moving liquid as it enters the magnetic field. Since these induced currents flow in a direction opposite to that of the current supplied through the conductors 54 and 56, they exert a breaking effect on the motion of the liquid. To minimize this the magnetic field intensity should be made to decrease gradually on both the upstream and downstream sides of the region in which the current is traversing the liquid. In the ideal case the falling off of field intensity would coincide with the falling off of current density due to the fringing of current in the liquid beyond the region where the conductors 54 and 56 are attached to the region 63 of the conduit. This distribution in field intensity is accomplished by the provision of spaces between the cores 32 and 34 and the conduit 30 beyond the ends of the region 63 thereof, as determined by the surfaces 68, 69, 70, and 71 on the cores.

Due to the flow of current across the conduit the magnetic field is distorted between the poles by introducing a component which increases the resultant field intensity on the upstream end and lowers it on the downstream end. This inhomogeneity in the field along the length of the conduit produces a greater counter electromagnetic force in the moving liquid on the upstream end than on the downstream side, with the result that the current distribution along the length of the tube is not uniform but is increased downstream and reduced upstream. Thus the resultant current and field distribution is such that the regions of highest current density are in regions of lowest field intensity.

The net result of this effect is to lower the pumping capacity. The magnitude of the effect will increase as the current density and the counter electromagnetic force in the liquid increase. For pumps of large cross-section, operating at relatively low currents, the effect is hardly noticeable, but for high rates of flow and accompanying large densities, field compensation should be provided. This is accomplished by tapering the poles at the conduit region 63 so that the magnetic gap is wider in the upstream end, as shown in Fig. 2. In addition, the conduit cross-section is progressively decreased so that the velocity of the liquid increases in the downstream direction at a rate such that the counter electromagnetic force in the liquid remains constant as the liquid traverses the region between the poles.

The progressive decrease in conduit cross-section is accomplished by progressively decreasing the dimension of the conduit 30 in the plane of the cores 32 and 34 as viewed in Fig. 2 in accordance with the decreasing spacing between the cores 32 and 34 at the conduit region 63. If the conduit 30 is made from a tube of originally uniform cross-sectional size, then the conduit region 63 progressively increases in width in the plane of the conductors 54 and 56 as shown in Fig. 1, but the increase is incidental.

The instant embodiment of the pump uses a conduit formed of a metal, such as stainless steel, high corrosion resistance and high electrical resistivity. The conduit wall thickness is 0.025 inch. The conduit tapers as it passes between the magnet poles or cores 32 and 34 from 1.80 inches to 1.43 inches in the downstream direction.

Its dimension in the current direction between the conductors 54 and 56 varies from 3.90 inches to 3.4 inches. The magnet gap also is tapered from a width of 1.86 inches at the entrance, or upstream end, to 1.50 inches at the exit, or downstream end. The pole pieces are 6 inches wide by 15 inches long, making a ratio of the pole lengths to the conduit width of 5:1.

As shown in Fig. 1, the conduit 30 extends through and beyond the extremities of the pump frame 18 and the coils 42 and 44. As previously mentioned, it is asgas 11,9 25

sumed that the liquid to be pumped moves through the conduit 30 from left to right as viewed in Fig. 1. Inasmuch as the pump is to be operated at temperatures well over 400 F., it is necessary to provide means to compensate for the expansion and contraction of the conduit 30 with respect to the system to which the pump is connected. Accordingly, each end of the conduit is provided with an expansion unit. As best seen in Fig. 8, an expansion unit 84 at the discharge or downstream end of the conduit 30 comprises a sleeve 85, a bellows 86, and a coupling 87. One end of the bellows is joined to the coupling through an adaptor ring 88. The other end of the bellows is joined by means of an adaptor ring 89 to the sleeve 85 which lies within the bellows and has one end free of and adjacent the coupling 87. The end of the bellows to which the sleeve is attached is joined to the discharge end of the conduit 30 by means of the adaptor ring 89 and another adaptor ring 90. An expansion unit 90a at the intake end of the conduit 30 has the same parts as the expansion unit 84, but the sleeve 85 is attached to the end of the bellows 86 joined to the coupling 87 rather than to the end of the bellows joined to the conduit 30 and is free of the conduit 30. The various parts joined together as aforesaid are joined by welding. Now as heating of the conduit 30 occurs with operation, the resultant lengthening thereof may take place without difficulty or involvement, because the sleeve 85 at the discharge end of the conduit may move freely with respect to the associated coupling 87 and the other sleeve 85 may move freely with respect to the inlet end of the conduit. The two bellows 86 contract as the conduit 30 expands and prevent escape of the liquid metal being pumped.

The entire assembly is mounted within an enclosure 91 which includes the base plate 12, a top plate 92, two oppositely disposed side plates 93 and 94, two oppositely disposed end plates 95 and 96, tubular extensions 97 and 98 and associated closures 99 and 100 housing and supporting the expansion units 84 and 90a, and bellows sleeves 101 and 102 secured to the top and bottom plates 92 and 12 by rings 103 and surrounding the connectors 48 and 46. The various parts of the enclosure 91 are welded to one another and the bellow sleeves 101 and 102 are secured to the connectors 48 and 46 by pressure sealing assemblies 104 so that the enclosure 91 is fluidtight and will prevent the escape of liquid metal being pumped in the event of failure of the conduit 30. If desired, an inert gas may be circulated in the enclosure through an inlet 105 in the top plate 92 and an outlet 106 in the bottom plate 12. The inlet 105 and the outlet 106 may also be used for the insertion of thermocouples that will prevent the application of electric power to the pump of the present invention when no liquid metal is in the conduit 30 so that the conduit will not burn up. The bellows sleeves 101 and 102 permit the connectors 48 and 46 to expand because of heating due to operation. The high temperatures at which the pump is to operate require all the parts of the enclosure 91 including the sealing assemblies 104 to be of metal. Thus the enclosure 91 provides a current path between the connectors 48 and 46. However, the resistance of this path is relatively high in comparison to that across the coils 44 and 42, the conductors 54 and 56, the conduit 30, and the liquid metal therein, because the enclosure parts are made of steel and the coils and conductors are of copper, and so the current flowing through the enclosure parts does not interfere with operation of the pump. Braces 107 help to secure the tubular extensions 97 and 98 to the end plates 95 and 96 of the enclosure 91. Tubular members 108 and 109, which are welded to the top and bottom plates 92 and 12, surround the bellows sleeves 101 and 102 so as to protect them.

Other variations of and applications for the present invention will be apparent to those skilled in the art and the invention is, therefore, to be limited only by the scope of the appended claims.

What is claimed is:

1. A direct-current electromagnetic pump for liquid metal comprising a conduit for the metal, means associated with the conduit for conducting an electric current therethrough at right angles to the conduit axis, and magnetic means associated with the conduit for passing a magnetic field therethrough at right angles to the conduit axis and to the electric current, the magnetic means including two poles oppositely disposed on either side of the conduit and in abutment therewith, each end of each pole being angled away from the conduit so that the pole faces are farther apart at the pole ends than at their centers.

2. A direct-current electromagnetic pump for liquid metal comprising a conduit for the metal, conductors engaging the conduit for conducting an electric current therethrough at right angles to the conduit axis, magnetic means associated with the conduit for passing a magnetic field therethrough at right angles to the conduit axis and the electric current, the magnetic means including two poles oppositely disposed on either side of the conduit and having central regions in abutment therewith, each end of each pole being angled away from the conduit beyond the region thereof abutted by the conductors so that the pole faces are farther apart at their pole ends than at their central regions.

3. A direct-current electromagnetic pump for liquid metal comprising a conduit for the metal, means associated with the conduit for conducting an electric current therethrough at right angles to the conduit axis, and magnetic means associated with the conduit for passing a magnetic field therethrough at right angles to the conduit axis and to the electric current, the magnetic means including two poles oppositely disposed on either side of the conduit and in abutment therewith, the pole faces being tapered so that they are farther apart at their upstream end than at their downstream end.

4. A direct current electromagnetic pump for liquid metal having a conduit for the metal, means associated with the conduit for conducting an electric current therethrough at right angles to the conduit axis and to the magnetic field, magnetic means associated with the conduit for passing a magnetic field therethrough at right angles to the conduit axis, the magnetic means including two poles having faces oppositely disposed on either side of the conduit and each having regions in abutment therewith, each end of each pole being angled away from the conduit so that the pole faces are farther apart at the pole ends than at said regions, the conduit being tapered in said region so that the cross-sectional area of the conduit in said region is greater at its upstream end than at its downstream end and the space between the magnetic pole faces being tapered so that the pole faces are farther apart at the upstream end of said region than at said downstream end of said region.

5. A direct current electromagnetic pump for liquid metal having a conduit for the metal, conductors contacting the conduit for conducting an electric current therethrough at right angles to the conduit axis and to the magnetic field, magnetic means associated with the conduit for passing a magnetic field therethrough at right angles to the conduit axis, the magnetic means including two poles oppositely disposed on either side of the conduit and in abutment therewith along the same region of the conduit as contacted by said conductors, each end of each pole being angled away from the conduit beyond the region thereof contacted by the conductors so that the pole faces are farther apart at their pole ends than at the regions which abut the conduit, the conduit along said region being tapered so that its cross-sectional area is greater at the upstream end of said region than at the downstream end of said region, and the space between the magnetic pole faces being tapered so that the pole 7 faces are farther apart at the upstream end of said region 2,386,369 than at the downstream end of said region. 2,612,109 2,645,279 References Cited in the file of this patent UNITED STATES PATENTS 126,947 2,224,505 Unger Dec. 10, 1940 698,623

8 Thompson Oct. 9, 1945 Wakefield Sept. 30, 1952 Rossman July 14, 1953 FOREIGN PATENTS Great Britain Dec. 24, 1919 Great Britain Oct. 21, 1953 

